1. Field of the Invention
This invention relates generally to oilfield wellbores and more particularly to wellbore systems and methods for the use of flowable devices in such wellbores.
2. Background of the Art
Hydrocarbons, such as oil and gas, are trapped in subsurface formations. Hydrocarbon-bearing formations are usually referred to as the producing zones or oil and gas reservoirs or “reservoirs.” To obtain hydrocarbons from such formations, wellbores or boreholes are drilled from a surface location or “well site” on land or offshore into one or more such reservoirs. A wellbore is usually formed by drilling a borehole of a desired diameter or size by a drill bit conveyed from a rig at the well site. The drill string includes a hollow tubing attached to a drilling assembly at its bottom end. The drilling assembly (also referred to herein as the “bottomhole assembly” or “BHA”) includes the drill bit for drilling the wellbore and a number of sensors for determining a variety of subsurface or downhole parameters. The tubing usually is a continuous pipe made by joining relatively small sections (each section being 30–40 feet long) of rigid metallic pipe (commonly referred to as the “drill pipe”) or a relatively flexible but continuous tubing on a reel (commonly referred to as the “coiled-tubing”). When coiled tubing is used, the drill bit is rotated by a drilling motor in the drilling assembly. Mud motors are most commonly utilized as drilling motors. When a drill pipe is used as the tubing, the drill bit is rotated by rotating the drill pipe at the surface and/or by the mud motor. During drilling of a wellbore, drilling fluid (commonly referred to as the “mud”) is supplied under pressure from a source thereof at the surface through the drilling tubing. The mud passes through the drilling assembly, rotates the drilling motor, if used, and discharges at the drill bit bottom. The mud discharged at the drill bit bottom returns to the surface via the spacing between the drill string and the wellbore (also referred herein as the “annulus”) carrying the rock pieces (referred to in the art as the “cuttings”) therewith.
Most of the currently utilized drilling assemblies include a variety of devices and sensors to monitor and control the drilling process and to obtain valuable information about the rock, wellbore conditions, and the matrix surrounding the drilling assembly. The devices and sensors used in a particular drilling assembly depend upon the specific requirements of the well being drilled. Such devices include mud motors, adjustable stabilizers to provide lateral stability to the drilling assembly, adjustable bends, adjustable force application devices to maintain and to alter the drilling direction, and thrusters to apply desired amount of force on the drill bit. The drilling assembly may include sensors for determining (a) drilling parameters, such as the fluid flow rate, rotational speed (r.p.m.) of the drill bit and/or mud motor, the weight on bit (“WOB”), and torque of the bit; (b) borehole parameters, such as temperature, pressure, hole size and shape, and chemical and physical properties of the circulating fluid, inclination, azimuth, etc., (c) drilling assembly parameters, such as differential pressure across the mud motor or BHA, vibration, bending, stick-slip, whirl; and (d) formation parameters, such as formation resistivity, dielectric constant, porosity, density, permeability, acoustic velocity, natural gamma ray, formation pressure, fluid mobility, fluid composition, and composition of the rock matrix.
During drilling, there is ongoing need to adjust the various devices in the drill string. Frequently, signals and data are transmitted from surface control units to the drilling assembly. Data and the sensor results from the drilling assembly are communicated to the surface. Commonly utilized telemetry systems, such as mud pulse telemetry and acoustic telemetry systems, are relatively low data rate transfer systems. Consequently, large amounts of downhole measured and computed information about the various above-noted parameters is stored in memory in the drilling assembly for later use. Also, relatively few instructions and data can be transmitted from the surface to the drilling assembly during the drilling operations.
After the well has been drilled, the well may be completed, i.e., made ready for production. The completion of the wellbore requires a variety of operations, such as setting a casing, cementing, setting packers, operating flow control devices, and perforating. There is need to send signals and data from the surface during such completion operations and to receive information about certain downhole parameters. This information may be required to monitor status and/or for the operation of devices in the wellbore (“downhole devices”), to actuate devices to perform a task or operation or to gather data about the subsurface wellbore completion system, information about produced or injected fluids or information about surrounding formation. After the well has started to produce, there is a continuous need to take measurements of various downhole parameters and to transmit downhole generated signals and data to the surface and to receive downhole information transmitted from the surface.
The present invention provides systems and methods wherein discrete flowable devices are utilized to communicate surface-generated information (signals and data) to downhole devices, measure and record downhole parameters of interest, and retrieve from downhole devices, and to make measurements relating to one or more parameters of interest relating to the wellbore systems.